Arrangement including an electronic flash tube

ABSTRACT

The invention relates to an arrangement including an electronic flash tube and a controlled semiconductor rectifier for extinguishing this tube. In order to extinguish the flash tube in a known arrangement, it is shunted by a semiconductor rectifier producing a short circuit across the tube. A drawback thereof is that the supply source of the arrangement a needlessly and heavily loaded thereby. In an arrangement according to the invention an auxiliary capacitor is used which receives a voltage larger than the supply voltage of the arrangement. When the instant of extinguishing has come the voltage of this auxiliary capacitor used to extinguish a further controlled rectifier arranged in series with the tube. Consequently, the supply source of an arrangement according to the invention is much less heavily loaded and in addition the arrangement is sooner ready for the next flash.

United States Patent Exner [451 Oct. 3, 1972 ARRANGEMENT INCLUDING AN ELECTRONIC FLASH TUBE [72] Inventor: Emil August Exner, Nijmegen,

Netherlands [73] Assignee: U.S. Philips Corporation, New

York, NY.

[22] Filed: Nov. 3, 1970 [21] Appl. No.: 86,522

[30] Foreign Application Priority Data Nov. 8, 1969 Netherlands ..6916884 [52] US. Cl. ..315/151, 315/241 P [51] int. Cl. ..H05b 37/00 [58] Field of Search ...3l5/241 P, 151, 159, 241, 243

[56] References Cited UNITED STATES PATENTS I 3,568,582 3/1971 Vchida et a1. ..315/241 P 3,418,904 12/1968 Wick et a1. ..95/10 3,473,084 10/1969 Dodge ..315/151 Primary Examiner-Nathan Kaufman Attorney-Frank R. Trifari ABSTRACT The invention relates to an arrangement including an electronic flash tube and a controlled semiconductor rectifier for extinguishing this tube.

In order to extinguish the flash tube in a known arrangement, it is shunted by a semiconductor rectifier producing a short circuit across the tube. A drawback thereof is that the supply source of the arrangement a needlessly and heavily loaded thereby.

In an arrangement according to the invention an auxiliary capacitor is used which receives a voltage larger than the supply voltage of the arrangement. When the instant of extinguishing has come the voltage of this auxiliary capacitor used to extinguish a further controlled rectifier arranged in series with the tube.

Consequently, the supply source of an arrangement according to the invention is much less heavily loaded and in addition the arrangement is sooner ready for the next flash.

10 Claims, 1 Drawing Figure PATENTEDnm 3 I972 EMIL A. EXNER AGENT R ARRANGEMENT INCLUDING AN ELECTRONIC I FLASH TUBE This invention relates to an arrangement including an electronic flash tube and a controlled semiconductor rectifier for extinguishing said tube, a control circuit of said controlled semiconductor rectifier including a photosensitive member, all this in such a manner that the flash duration in influenced as a function of the brightness of an object exposed by the tube, the arrangement being intended to be supplied with a direct current.

' A known arrangement of the above-mentioned kind is described, for example, in the publication Thyristor-Elektronik im Blitzergrat from'Funkschau 1969, Vol. 18, pages 623-624.

Arrangements as described in this publication have the advantage that the flash duration depends on the distance from the flash tube to an object to be photographed and also on the color of the relevant object. In fact, when a certain quantity of light is directed onto the object, the photosensitive arrangement in the central circuit of the controlled semiconductor rectifier will extinguish the flash tube in response to a reflected portion of this quantity of light. In the mentioned publication thecontrolled semiconductor rectifier is shunted across the flash tube. A drawback of this known embodiment is that the supply capacitor of the flash tube is substantially discharged when the flash tube is extinguished.

An object of the present invention is to provide a circuit arrangement in which less energy is to be derived from the supply arrangement of the flash tube and in which a satisfactory extinguishing procedure of the flash tube may still be achieved.

According to the invention there is provided an arrangement including an electronic flash tube and a controlled semiconductor rectifier for extinguishing said tube and a control circuit for said controlled semiconductor rectifier including a photosensitive member, all this combined in a manner such that the flash duration is controlled as a function of the brightness of an object exposed by the tube. The arrangement is intended to be supplied with a direct current and is characterized in that the positive input terminal is connected to the negative input terminal of the arrangement by means of a series arrangement of at least a second controlled semiconductor rectifier and the flash tube, the tube prior to flashing being shunted by a second series arrangement which includes at least one chargeable element and a further circuit element, said further circuit element being highly resistive at least during flashing and the first controlled semiconductor rectifier being connected to the junction of the chargeable element and the further circuit element, the other side of the last-mentioned controlled semiconductor rectifier being connected to the positive input terminal of the arrangement, and the voltage across the chargeable element being directed oppositely to and being larger than the voltage on the input terminals of the arrangement at least a moment after the commencement of a flash so that the chargeable element has a voltage by which the second controlled semiconductor rectifier can be extinguished when the first controlled semiconductor rectifier is rendered conducting.

An advantage of an arrangement according to the invention is that no energy is derived from the supply device of the arrangement when the flash tube is extinguished. A further advantage is that no further energy is derived from the chargeable element after the second controlled rectifier has been extinguished.

An advantage of these features mentioned in the previous paragraph is that the arrangement can operate with a greater efficiency and in addition the arrangement is quickly ready again for supplying the next flash. In addition, the face that energy is not needlessly derived from the supply source has the advantage that this source will be less quickly exhausted.

The chargeable element may be, for example, a small battery. This chargeable element may be alternatively formed by a capacitor which is first charged by a separate direct current source.

In an advantageous embodiment of an arrangement according to the invention, the arrangement is fed by a previously charged main capacitor and the chargeable element in the second series circuit is an auxiliary capacitor. The side of the auxiliary capacitor remote from the further circuit element is connected to the positive input terminal of the arrangement by means of a third series arrangement composed of a diode and a resistor.

An advantage of this preferred embodiment is that the auxiliary capacitor is first charged already to substantially the same voltage as that of the main capacitor, that is to say, before flashing takes place. When flashing takes place subsequently, the voltage on the main capacitor will decrease because this main capacitor supplies the flashing energy. When, after some time, the first controlled semiconductor rectifier is rendered conducting through the photosensitive member, the voltage on the auxiliary capacitor will be larger than that on the main capacitor. Then the voltage at the junction of the auxiliary capacitor and the further circuit element will be brought to a positive potential so that the auxiliary capacitor supplies a current having a direction opposite to the forward direction of the second controlled semiconductor rectifier which will be extinguished thereby.

Instead of the mentioned second controlled semiconductor rectifier, a cascade circuit of two or more thyristors may be used optionally.

The further circuit element in the second series arrangement shunting the flash tube preferably comprises a resistor in series with a diode. An advantage thereof is that no switching element need be present in this second series arrangement and that the auxiliary capacitor cannot be discharged across the tube.

However, when the further circuit element is formed as a switching element, a preferred embodiment according to the invention is obtained if this switching element is coupled to the shutter mechanism of a photo-camera in a manner such that this switching element is closed in the closed condition of the shutter and is open in the open condition of the shutter.

An advantage thereof is that the auxiliary capacitor (or any other chargeable element) is more rapidly charged after taking a flash photograph so that it is also possible to take the next flash photograph more rapidly.

In order that the invention may be readily carried into effect, a few embodiments thereof will now be described in detail, by way of example with reference to the accompanying diagrammatic drawing, the single figure .of which shows an electric circuit of a flash tube ignition control circuit according to the invention. In the drawing the reference numerals 1 and 2 denote the input terminals of an arrangement according to the invention. The terminals 1 and 2 can receive current through an auxiliary arrangement including a main capacitor 3. This main capacitor 3 is previously charged by a device not further shown whose terminals are denoted by the reference numerals 4, 5.

The terminals 1 and 2 are connected by means of a series arrangement of a thyristor 6, a coil 7 and an electronic flash tube 8. The junction of thyristor 6 and coil 7 is connected to the control electrode of afurther thyristor 9. The thyristor 9 together with a coil l'are connected in parallel with the series arrangement of thyristor6 and coil 7. The combination 6, 7, 9, 10 is referred to as a cascade circuit. The flash tube 8 is shunted by a series arrangement of a coil .11, a capacitor 12, a resistor 13 and a diode 14. The junction of capacitor 12 and resistor 13 is connected to a cathode of a controlled semiconductor rectifier (thyristor) 15. The anode of this thyristor 15 is connected to the input terminal 1 of the arrangement. Furthermore, there is provided a series arrangement of a diode 16 and a resistor 17. The latter. series arrangement is connected at one end to the terminal 1 of the arrangement and at the other end to a junction of coil 11 and capacitor 12. The reference numeral 18 denotes a terminal which is connected to the control electrode of thyristor 6 and the reference numeral 19 denotes a terminal which is connected to the junction of coil 7 and tube 8. In addition the Figure shows a control electrode of the tube 8, which electrode is denoted by the reference numeral 20..

The control circuit of thyristor 15 includes, inter alia: an energy source, for example, a battery 21. This energy source 21 is connected in series with a photosensitive element 22 and a variable resistor 23. The negative terminal of energy source 21 is connected through a switch 24 to the cathode of thyristor 15. The control electrode of thyristor 15 is connected to the variable resistor 23. Furthermore, a capacitor 25 and a variable resistor 26 are connected in parallel between the con trol electrode and the cathode of thyristor 15.

The circuit described operates as follows: First the main capacitor 3 is charged up through the terminals 4, 5 via a device, not shown. Simultaneously, the auxiliary capacitor 12 is charged to the same voltage as that of the capacitor 3 through diode 16 and resistor 17. Subsequently, a voltage is applied between the points 18 and 19 and the trigger electrode of the tube 8 when a shutter mechanism of a photocamera is actuated. The shutter mechanism also closes the switch 24 in the con trol circuit of thyristor 15. The result of all this is that the thyristor 6 (and 9) begins to conduct and the flash tube 8 is ignited. In this case the main capacitor 3 will partially be discharged across the series circuit 1, 6, 7 (9, l0), 8, 2. The light emitted by the flash tube 8 is partly incident on an object to be photographed and is subsequently reflected and is incident on the photosensitive member 22 in the control circuit of thyristor 15. When the quantity of light thus reflected has reached a certain threshold value, the thyristor 15 will be rendered conducting, namely because capacitor has received a given voltage. The result thereof is that the junction between capacitor 12 and resistor 13 is brought to the positive potential of the input terminal 1. Meanwhile the capacitor 2, which has maintained. its initial voltage, now has a higher voltage than that of the main capacitor 3. The result is that an opposite current starts to flow from capacitor 12 through coil 11, is distributed over the two parallel branches 7, 6, and 10, 9, respectively, and subsequently flows to thyristor 15 and then again to the other electrode of capacitor 12. Considering the fact that this capacitor 12 had a higher initial voltage than the instantaneous value of the voltage of capacitor 3, this current is sufficient to extinguish the two thyristors 6 and 9. Consequently the flash tube 8 is extinguished. The capacitor 12 cannot be discharged through a different path and this is due to the presence of diode 14. When the thyristors 6and 9 become non-conducting no further energy is derived from the main capacitor 3. At the most some current is derived from capacitor 3 so as to bring capacitor 12 to the same voltage as that on capacitor 3. A great advantage of this invention is that in the first place main capacitor 3 is not discharged to a zero value and in addition capacitor 12 need not always be discharged to a voltage of zero. This means that all energy may be utilized advantageously. All this may lead to a longer lifetime of the supply source of the flashing arrangement.

Optionally, the combination of resistor 13 and diode 14 might be replaced by a switching element (for example, a mechanical switch or a transistor) which switching element is operated (in a manner not further shown) simultaneously with the previously mentioned shutter mechanism of the photocamera and thus also simultaneously with the switch 24.'However, in this case the switching element (at the position of 13 and 14) is closed when no flash photograph is taken (shutter closed) and is opened when the flash photograph is taken. In the closed condition of this switching element the capacitor 12 can be charged through this switching element. In the open condition of this switching element the auxiliary capacitor 12 is prevented from being discharged through the flash tube 8.

In a practical embodiment (the circuit of the Figure) the main capacitor 3 had a capacitance of approximately 550 uuF and the capacitor 12 had a value of approximately 40 ,u.uF. The resistors 17 and 13 had values of 10 kOhms and kOhms, respectively. The inductors 7, 10 and 11 had values of 0.2 ,uuH, 0.2 rul-I and 60 ml-l, respectively. The initial voltage across the main capacitor 3 was approximately 350 Volts.

What is claimed is:

1. An ignition control circuit for an electronic flash tube comprising, first and second input terminals adapted to be connected to a source of DC voltage, first and second semiconductor controlled rectifiers, means serially connecting said first controlled rectifier and the flash tube to said first and second input terminals, at least one chargeable elementand a further circuit impedance element serially connected in shunt with said flash tube prior to the tube flash, said further circuit element exhibiting a high impedance at least during the flash period of the tube, means connecting the second controlled rectifier between the first input terminal and the junction of the chargeable element and the further circuit element, a control circuit including a photosensitive member coupled to the control electrode of said second controlled rectifier, said photosensitive member being arranged to respond to the flash tube light reflected thereto by an object exposed to the tube flash such that the second controlled rectifier is triggered into conduction as a function of the brightness of said object thereby to extinguish the flash tube and thus limit the flash duration as a function of the object brightness, and means for applying an electric charge to said chargeable element of a polarity opposed to that of the input terminals and of a magnitude that is larger than the voltage at the input terminals at a moment after the flash tube is ignited whereby the voltage of the chargeable element is capable of extinguishing the first controlled rectifier when the second controlled rectifier is triggered into conduction.

2. An ignition circuit as claimed in claim 1 further comprising a main capacitor connected across the input terminals and directly charged by the DC voltage applied thereto, and wherein the chargeable element comprises an auxiliary capacitor and said charge applying means comprises a series arrangement of a diode and a resistor connected between the first input terminal and the side of the auxiliary capacitor that is remote from said further circuit element.

3. An ignition circuit as claimed in claim 1 wherein the further circuit element comprises a resistor in series with a diode.

4. An ignition circuit as claimed in claim 1 wherein the further circuit element comprises a switch which is coupled to the shutter mechanism of a photocamera in a manner such that said switch is closed in the closed condition of the shutter and is open in the open condition of the shutter.

5. An ignition control circuit for a flash discharge tube comprising, a pair of input terminals adapted to be connected to a source of DC voltage, a supply capacitor connected across said input terminals so as to be charged to a given ignition voltage, a first controlled switching element connected in series with the flash tube across said input terminals, an auxiliary capacitor, impedance means, means connecting the auxiliary capacitor and the impedance means in a series circuit across the terminals of the flash tube, a second controlled switching element connectedin series with said impedance means across the input terminals, a photosensitive member arranged to respond to the flash tube light reflected thereto by an exposedobject, a control circuit including said photosensitive member coupled to a control electrode of the second switching element to trigger same into conduction at a time determined by the brightness of the exposed object thereby to extinguish the flash tube, and means for triggering said first switching element into conduction thereby to at least partially discharge the supply capacitor across the flash tube, said auxiliary capacitor being coupled to said first switching element to bias same into cut-off in response to conduction in the second switching element.

6. An ignition circuit as claimed in claim 5 further comprising a charge circuit coupling the auxiliary capacitor to the input terminals so that the uxiliary capacitor is charge up independently of said irst controlled switching element and with a polarity opposed to that of the voltage on the supply capacitor.

7. An ignition circuit as claimed in claim 6 wherein said second switching element comprises a thyristor and said impedance means comprises a first diode connected with the same polarity as the thyristor.

8. An ignition circuit as claimed in claim 7 wherein said charge circuit comprises a second diode connected in series with said auxiliary capacitor and said first diode across the input terminals and poled with the same polarity as the first diode.

9. An ignition circuit as claimed in claim 6 wherein said flash tube includes a trigger electrode and means for applying a trigger voltage thereto in synchronism with the triggering of said first switching element.

10. An ignition circuit as claimed in claim 5 wherein said impedance means comprises a diode poled so as to prevent the discharge of said auxiliary capacitor across the flash discharge tube. 

1. An ignition control circuit for an electronic flash tube comprising, first and second input terminals adapted to be connected to a source of DC voltage, first and second semiconductor controlled rectifiers, means serially connecting said first controlled rectifier and the flash tube to said first and second input terminals, at least one chargeable element and a further circuit impedance element serially connected in shunt with said flash tube prior to the tube flash, said further circuit element exhibiting a high impedance at least during the flash period of the tube, means connecting the second controlled rectifier between the first input terminal and the junction of the chargeable element and the further circuit element, a control circuit including a photosensitive member coupled to the control electrode of said second controlled rectifier, said photosensitive member being arranged to respond to the flash tube light reflected thereto by an object exposed to the tube flash such that the second controlled rectifier is triggered into conduction as a function of the brightness of said object thereby to extinguish the flash tube and thus limit the flash duration as a function of the object brightness, and means for applying an electric charge to said chargeable element of a polarity opposed to that of the input terminals and of a magnitude that is larger than the voltage at the input terminals at a moment after the flash tube is ignited whereby the voltage of the chargeable element is capable of extinguishing the first controlled rectifier when the second controlled rectifier is triggered into conduction.
 2. An ignition circuit as claimed in claim 1 further comprising a main capacitor connected across the input terminals and directly charged by the DC voltage applied thereto, and wherein the chargeable element comprises an auxiliary capacitor and said charge applying means comprises a series arrangement of a diode and a resistor connected between the first input terminal and the side of the auxiliary capacitor that is remote from said further circuit element.
 3. An ignition circuit as claimed in claim 1 wherein the further circuit element comprises a resistor in series with a diode.
 4. An ignition circuit as claimed in claim 1 wherein the further circuit element comprises a switch which is coupled to the shutter mechanism of a photocamera in a manner such that said switch is closed in the closed condition of the shutter and is open in the open condition of the shutter.
 5. An ignition control circuit for a flash discharge tube comprising, a pair of input terminals adapted to be connected to a source of DC voltage, a supply capacitor connected across said input terminals so as to be charged to a given ignition voltage, a first controlled switching element connected in series with the flash tube across said input terminals, an auxiliary capacitor, impedance means, means connecting the auxiliary capacitor and the impedance means in a series circuit across the terminals of the flash tube, a second controlled switching element connected in series with said impedance means across the input terminals, a photosensitive member arranged to respond to the flash tube light reflected thereto by an exposed object, a control circuit including said photosensitive member coupled to a control electrode of the second switching element to trigger same into conduction at a time determined by the brightness of the exposed object thereby to extinguish the flash tube, and means for triggering said first switching element into conduction thereby to at least partially discharge the supply capacitor across the flash tube, said auxiliary capacitor being coupled to said first switching element to bias same into cut-off in response to conduction in the second switching element.
 6. An ignition circuit as claimed in claim 5 further comprising a charge circuit coupling the auxiliary capacitor to the input terminals so that the auxiliary capacitor is charged up independently of said first controlled switching element and with a polarity opposed to that of the voltage on the supply capacitor.
 7. An ignition circuit as claimed in claim 6 wherein said second switching element comprises a thyristor and said impedance means comprises a first diode connected with the same polarity as the thyristor.
 8. An ignition circuit as claimed in claim 7 wherein said charge circuit comprises a second diode connected in series with said auxiliary capacitor and said first diode across the input terminals and poled with the same polarity as the first diode.
 9. An ignition circuit as claimed in claim 6 wherein said flash tube includes a trigger electrode and means for applying a trigger voltage thereto in synchronism with the triggering of said first switching element.
 10. An ignition circuit as claimed in claim 5 wherein said impedance means comprises a diode poled so as to prevent the discharge of said auxiliary capacitor across the flash discharge tube. 